The present invention relates to a device for adjustment of a rotor blade mounted on a rotor hub of a wind energy converter, to a corresponding method for adjusting a rotor blade of a wind energy converter, and to a wind energy converter.
Wind energy can be converted into useful forms, such as electricity, by a wind energy converter that generally includes a generator driven by a rotor, e.g. a low-speed propeller, rotatably supported at the upper end of a tower. The rotor typically includes a centrally positioned rotor hub and at least one rotor blade, which extends radially from the rotor hub.
Subject to the action of wind forces, wind energy converters are exposed to high stresses. One method of reducing the forces acting on the wind energy converter is to use rotor blade adjustment, wherein the rotor blades are rotatably attached to the rotor hub, such that each rotor blade can be turned around an axis of rotation approximately in the longitudinal direction of the blade, between an operation position, which enables the wind to drive the rotor, and a feathered position in which the rotor blade presents the least resistance to the wind. Rotor blade adjustment can also be used for braking the rotor by turning the rotor blades into the feathered position when the wind energy converter is to be shut down.
In wind energy converters according to the prior art, which for the most part have three rotor blades, the latter are usually adjusted by a central linear drive in combination with a mechanical rod. Newer systems use mechanical/electrical and mechanical/hydraulic individual blade adjustment drives, typically located in the rotor hub. In order to be able to quickly turn each rotor blade into a desired operating position during operation and into the feathered position for shutdown, the drive or drives must be dimensioned to provide a corresponding power output predetermined by the rotor blades and the loads thereof.
Basically the rotor blades are subjected to loads due to inertial forces, forces of gravity (the center of gravity of the rotor blades generally lies outside their axis of rotation) and the external wind forces. The wind forces act towards turning the rotor blades in the direction of the feathered position, while the inertial forces act in both directions according to the respective position of the rotor blades during one rotor revolution, the inertial forces mostly predominating. Turning of the rotor blades beyond the feathered position is conventionally limited by a mechanical stop. If the rotor blades are not stopped, such as in the event of failure of a blade adjustment drive, they execute an oscillating rotary motion around their axis of rotation over the course of one rotor revolution, preventing a shutdown of the wind energy converter. Even in a wind energy converter with individual blade adjustment drives for each rotor blade, where it may be possible to brake the rotor by turning only a subset of the rotor blades into the feathered position, failure to turn one of the blades will subject the wind energy converter to excessive and potentially damaging loads.
U.S. Pat. No. 6,939,103 discloses a wind power installation in which an adjusting device for adjusting the pitch angle of a rotor blade has at least two electric-motor drives for applying force for adjustment of the rotor blade. Each individual adjusting drive is over-sized so that, in a situation where one of the drives fails, a remaining drive can still be operated to bring the rotor blade into the feathered position. However, since the drives have to be dimensioned to provide more power output than is required in normal operation, the cost of the wind energy converter is considerably increased.
Likewise in a case of adjusting the rotor blades against spring force or hydraulic pressure that act into the direction of the feathered position, rotor blade adjustment drives must be expensively dimensioned for higher loads since the spring force or the force of hydraulics must also be overcome.
U.S. Pat. No. 6,428,274 discloses a device for adjustment of rotor blades of a wind power plant with a drive for turning the rotor blades and an activatable lockout connected to each rotor blade. In an activated state the lockout prevents turning of the rotor blades into the operating position but allows turning the rotor blades into the feathered position. In the event of the drive becoming inoperative due to a power failure, the lockout is activated to allow turning when the rotor, during its rotation, passes a region where external wind, gravitational and inertial forces combine to turn the blade in the direction of the feathered position, and to prevent turning when the rotor passes a region where external forces combine in the opposite direction. While the rotor blade may eventually reach the feathered position in this way, a considerable number of revolutions of the rotor may be required during which the wind energy converter is subjected to excessive and potentially damaging stresses because the blade has not yet reached the feathered position.